The field of the present invention is microbial production of hydrogen through the management of the anaerobic or nearly anaerobic metabolism of consortia of microorganisms, including archaea and bacteria, to produce hydrogen, either in-situ or ex-situ, from hydrocarbon substrates such as coal, carbonaceous shale, oil, tar sands, bitumen, peat, and the like.
Because of the clean burning nature of hydrogen and its energy density on a weight basis, it is highly valued as an energy source. Billions of dollars of research have been expended on the invention and refinement of hydrogen fuel cells which have none of the carbon emissions associated with the use of fossil fuels. The greatest single obstacle to the widespread use of hydrogen fuel cells for motor transport and electricity generation is the high cost of molecular hydrogen on a cost per Btu basis relative to gasoline, coal, and natural gas. The present invention can dramatically lower the cost of hydrogen by utilizing microbial consortia to generate that hydrogen from the vast resources of coal, carbonaceous shales, oil, tar sands, bitumen and peat available throughout the world.
Currently, hydrogen is generated primarily by reformulation of methane by exposure to high pressure, high temperature steam. Most of the hydrogen liberated in this reaction is used in combination with nitrogen to make fertilizer. However, the Btu value of the hydrogen produced is far less than the Btu value of the fuel needed to produce it, making this an expensive and endergonic reaction that frustrates the widespread use of hydrogen as a transportation or electrical generation fuel.
Unlike the substrates in the present invention, agricultural waste, compost, municipal wastes including sewage and waste waters have been utilized as starting materials for fermentations to yield hydrogen gas. For example, Clostridia have been identified as important microorganisms for the microbial production of hydrogen gas from agricultural wastes, other cellulosic materials and sewage (JP 07031998 (1995), Van Ginkel et al. (2000) Ann. Conf. & Expos. on Water Quality and Wastewater Treatment, Water Environment Federation, 3413-3429; Nazinia, Tenn. (1981) Mikrobiologiia 50:163-166). A wide variety of heterotrophic microorganisms are known to produce hydrogen gas from organic waste products. Photosynthetic microorganisms such as species of Rhodobacter, Rhodopseudomonas and Rhodospirillum have also been proposed as microorganisms useful in the microbial production of hydrogen. A potential disadvantage of using photosynthetic microorganisms for phototrophic generation of hydrogen relates to limitations imposed on the penetration of light into a reactor containing a relevant substrate or where the substrate is underground, such as in massive sub-bituminous coal deposits containing billions of tons of coal and billions of pounds of hydrogen.
Despite the advances that have been made towards producing hydrogen from agricultural and municipal wastes, the limited availability and inconsistent composition and quality of these materials as well as the cost of hydrogen production through this process have precluded their use to date as substrates for the microbial production of hydrogen at quantities that could create a significant alternative source of energy relative to traditional fossil fuels (i.e. crude oil, natural gas, and coal). Furthermore, even assuming a substantial increase in biomass devoted to H2 production, maximum total H2 generated from agricultural and municipal wastes can provide less than 5% of current U.S. energy demand.
Research on microbial hydrogen production has focused exclusively on the conversion of waste products that contain easily fermentable materials including polysaccharides (Wang et al. 2003). For example, a myriad of cellulose-containing wastes produced in the food processing industry, agriculture, and domestic sewage have been evaluated as substrates to support microbial hydrogen production. Cellulose and other polysaccharides are easily fermentable (to hydrogen, carbon dioxide, acetate, and other organic acids) by a number of well characterized microorganisms and metabolic pathways. However, arguments have been made that microbial hydrogen production using these substrates will require very high conversion rates and efficiencies that have not been attained by the tested microorganisms (see, e.g. Benemann (1996)).
Even though there have been substantial technological advances in fossil fuel production techniques, the majority of oil discovered in the world remains trapped in the subsurface. Trapped crude oil in oil reservoirs, coals that may be too deep to excavate or that contain levels of impurities too high to burn, and carbonaceous shales that provide only a small amount of natural gas relative to the total hydrogen and energy within them represent a large source of substrate for microbial conversion to hydrogen.
There are numerous oil fields within the United States and around the world that are at or near the point of abandonment due to the inability to continue to produce oil from them profitably. Under current technology and oil prices, those fields will be abandoned with billions of barrels of oil remaining in place since primary and secondary oil recovery techniques still normally leave behind half or more of the original oil in place in those reservoirs at the time they are abandoned. That remaining oil represents a significant quantity of substrate for the generation of hydrogen that would otherwise be lost.
Hydrocarbon-bearing formations have been noted to contain variable amounts of hydrogen gas. See, e.g., Khorunzhii et al. (1977) Ugol'Ukrainy 4:42-44; Kosenko et al. (1967) Geologichnii Zhurnal 27:83-87. Although there is apparent recognition of the presence of some hydrogen in coal formations, it is unusual to detect hydrogen in hydrocarbon deposits. The present inventors are not aware of reports that document the microbial production of hydrogen from these materials or of commercial operations in which hydrogen is produced by microbial metabolism in coal-bearing or other hydrocarbon-rich environments.
By managing the metabolism of microorganisms to generate hydrogen, large amounts of that clean fuel can be made available for use. The substrate for that hydrogen generation is available in vast quantities in the form of coal, carbonaceous shale, tar sands, bitumen, peat, and the remaining oil in underground reservoirs.